The present invention relates to an improved form of gravity separator for mixtures of immiscible liquids of different densities, such as, for example, oil and water.
More specifically, the invention is an improved gravitational separator of the type utilizing a collection tank or housing for receiving a mixture of the fluids to be gravitationally separated, the tank having either a floating dome or diaphragm element within the upper area of the tank which serves as a reaction surface against which the volume of lighter (less dense) fluid accumulated within the upper portion of the tank exerts an upward, buoyant influence.
Separators of the type utilizing a floating dome are known in the prior art, as exemplified in the British patent specification No. 1,212,553 to Cornelis in'tVeld published Nov. 18, 1970 and U.S. Pat. No. 3,628,660, also to in'tVeld, granted Dec. 21, 1971. In separators of this type, the mixture of lighter and heavier fluids (oil and water, generally) is admitted to the interior of the separator beneath the dome under positive pressure or is inducted therein by suction of the heavier fluid from the heavier fluid discharge pipe of the separator, with the separator being hermetically sealed. The mixture of heavier and lighter fluids gravitationally separate in the separator, with lighter fluid rising up under the dome and heavier fluid sinking to the lower part of the separator vessel beneath the dome.
The gradual accumulation of lighter fluid beneath the dome, which is counterbalanced so as to normally be slightly negatively buoyant in the heavier fluid, causes the dome to float upwardly in the heavier fluid within the separator. It is customary to sense the high limit position of the dome to produce a control signal useful to instigate valve and pump actuations which enable the removal of less dense separated fluid from beneath the dome.
Gravitational separators of this type that are used to separate oil from an oily water mixture are provided with filter or coalescer screens or elements between the lower part of the separator and the water discharge pipe to collect any lingering droplets of oil carried to the lower part of the separator. Such screens are backwashed periodically to remove the oil clinging to the coalescers and, as described in the above-referenced U.S. Pat. No. 3,628,660, such backwashing of the screens can be carried out quite efficiently during the oil discharge mode of separator operation. That is, it is customary procedure to remove the accumulated oil from beneath the floating dome by pressurizing the clean water discharge pipe of the separator to admit clean water backwards into the lower end of the separator through the coalescer screens, and into the area beneath the dome to thereby force accumulated oil out of the separator under positive pressure. Only oil is discharged, of course, the reverse inflow of water being ceased when the accumulated oil has been discharged and the dome has sunk to its lower starting level.
Several problem areas have been encountered with the use of separators of the type just described. There has arisen, for example, a need for a simple, efficient and substantially failsafe system to precisely counterbalance the floating dome or the diaphragm beneath which the separated oil is trapped and to accurately sense when the volume of separated oil has reached an upper limit within the separator so that removal procedures can be instigated. Particularly in instances where the specific gravity of the oil to be separated is close to the density of water, a need for an extremely precise means for measuring a predetermined volume of accumulated oil is necessary to ensure proper functioning of the separator. Also, flow of water through the coalescer screens has been found to be less than ideal both in a forward and reverse flush sense. Ideally, flow in a forward direction through the coalescer screens should be uniform across all of the screens in the system and when the screens are backflushed, the backflush flow should occur entirely across the surfaces of the coalescer screens to remove oil droplets therefrom and furthermore, the discharge of oil from between the coalescer screens should be as complete as possible during the backflush operation. Finally, it has been found to be highly desirable to prevent any accumulation of oil above the separator dome (or diaphragm) during the operating life of the separator, since accumulation of the less dense fluid above the dome causes an inaccurate flotation response of the dome to the accumulated oil beneath the dome.
One approach to the dome counterbalance problem has been described in U.S. Pat. No. 3,957,638 assigned to the assignee of the instant application. In this patent, which is incorporated herein by reference, a complete description is provided of a prior art dome balancing system and separator control system which the present invention is intended to improve upon. It should be noted that, although not illustrated in that patent, the prior art balancing and control system was pneumatically operated. The complex balancing system of levers, weights, pivoted shafts, bearings and seals was found to be cumbersome and heavy as well as costly to fabricate. Moreover, an electronic control system has been found to be far more desirable than the electrical system illustrated in that patent and the pneumatic system previously in use.
The present invention finds particular application in a bilge water disposal system for a vessel, such as described in copending U.S. application Ser. No. 530,539 filed Dec. 9, 1974 by the inventors Chester H. Walters (one of the present co-inventors), Harold J. Barmeier, Jr. and Greig Sullivan, that application having been assigned also to the assignee of the present invention, and which is intended to be incorporated herein by reference. Other applications of the present invention, of course, are envisioned in static, industrial installations for separating mixtures of immiscible fluids of different densities.